1. Field of the Invention
This invention relates to an apparatus for recording and reproducing information on and from a recording medium formed with a wobbling track and pre-pits.
2. Description of the Related Art
Optical discs include a DVD-R (DVD Recordable) and a DVD-RW (DVD Rewritable). Each of the DVD-R and the DVD-RW has a disc member formed with a spiral of a wobbling groove on and from which main information can be recorded and reproduced. The wobble of the groove indicates first auxiliary information recorded on the disc member. The first auxiliary information contains a reference clock signal. The disc member has land portions between neighboring groove portions. A groove portion and a pair of land portions adjoining the groove portion compose a track portion. Second auxiliary information (land pre-pit signals) is previously recorded on the land portions. Specifically, the second auxiliary information is represented by land pre-pits formed in the land portions. The second auxiliary information contains address information from which the position of an arbitrary point on the disc member can be detected.
During the recording of main information on the DVD-R or the DVD-RW or the reproduction of main information therefrom, the track is scanned by a laser beam while the disc is rotated. In this case, the wobble of the groove in the track and the pre-pits in the lands in the track are detected. A wobble signal is generated in response to the detection of the wobble of the groove. The reference clock signal is reproduced from the wobble signal. Rotation of the disc is controlled in response to the reproduced reference clock signal. Land pre-pit signals are generated in response to the detection of the pre-pits. The position of a currently-accessed point on the disc is detected from the land pre-pit signals.
The generation of the land pre-pit signals is implemented as follows. The wobble of the groove and the positions of the pre-pits in the lands are in a predetermined phase relation. A reflected laser beam coming from the disc is converted into an electric signal. A wobble signal is extracted from the electric signal. The wobble signal has a level which alternates in accordance with the wobble of the groove. Spike-like peak signals caused by the pre-pits are superimposed on the wobble signal. The wobble signal is compared with a reference signal of a fixed threshold level so that high-level portions of the wobble signal which exceed the threshold level are selected. A gate signal synchronous with the wobble signal is generated. AND operation is executed between the gate signal and the high-level portions of the wobble signal, thereby extracting the spike-like peak signals from the high-level portions of the wobble signal. The extracted spike-like peak signals constitute the land pre-pit signals.
Japanese patent application publication number 10-320781 discloses an apparatus for detecting pre-pit signals. In the apparatus of Japanese application 10-320781, a first wobble signal is extracted from the output signal of an optical pickup. Pre-pit signals each having a spike-like waveform are superimposed on the first wobble signal. A PLL-based servo circuit generates a sync signal in response to the first wobble signal. The sync signal is equal in phase and frequency to the first wobble signal. The sync signal periodically peaks. A timing of every peak of the sync signal coincides with a moment at which a pre-pit signal is expected to be superimposed on the first wobble signal. The sync signal is basically equal in waveform to the first wobble signal except spike-like components corresponding to pre-pit signals. The first wobble signal is biased by a reference voltage, being changed into a second wobble signal. The second wobble signal and the sync signal are compared with each other so that the pre-pit signals are extracted or detected. In the case where the second wobble signal has a noise component at a time position near a pre-pit signal, it tends to be difficult to discriminate the pre-pit signal from the noise component.
Japanese patent application publication number 10-241260 discloses an apparatus for recording information on a DVD-R. In the apparatus of Japanese application 10-241260, a first wobble signal is extracted from the output signal of an optical pickup. Pre-pit signals each having a spike-like waveform are superimposed on the first wobble signal. The first wobble signal is subjected to an amplitude limiting process responsive to an upper limiting signal and a lower limiting signal so that pre-pit signals in the first wobble signal are suppressed. The upper limiting signal and the lower limiting signal are generated from the first wobble signal. Accordingly, the upper limiting signal and the lower limiting signal depend on the first wobble signal. The limiting-resultant wobble signal, which is called a second wobble signal, propagates through a band pass filter tuned to a true wobble frequency. The band pass filter attenuates the pre-pit signals in the second wobble signal. The output signal from the band pass filter is referred to as a final wobble signal. The final wobble signal is binarized into a reference clock signal used for the control of rotation of the DVD-R. In the case where the pre-pit signals remain in the final wobble signal to a considerable degree, the reference clock signal tends to have an unacceptable frequency error.
It is a first object of this invention to provide an information recording and reproducing apparatus which can reliably discriminate pre-pit signals from noise signal components.
It is a second object of this invention to provide an information recording and reproducing apparatus which can reliably separate a true wobble signal from pre-pit signals and noise signal components.
A first aspect of this invention provides an apparatus for recording and reproducing information on and from a recording medium formed with a track and pre-pits, the track having a wobble, the pre-pits being in a predetermined phase relation with the wobble of the track. The apparatus comprises a pickup for reproducing a signal from the recording medium; a limiter for limiting an amplitude of the signal reproduced by the pickup in response to a limiting level, and thereby processing the signal reproduced by the pickup into a limiting-resultant signal; a filter for suppressing components of the limiting-resultant signal generated by the limiter, and thereby processing the limiting-resultant signal into a filtering-resultant signal, the components having specified frequencies and being caused by the pre-pits; first means for generating the limiting level for the limiter in response to the filtering-resultant signal generated by the filter; and second means for extracting, from the filtering-resultant signal generated by the filter, a signal caused by the wobble of the groove.
A second aspect of this invention is based on the first aspect thereof, and provides an apparatus further comprising third means for controlling the limiting level for the limiter in response to whether the apparatus is operating in a recording mode or a reproducing mode.
A third aspect of this invention provides an apparatus for recording and reproducing information on and from a recording medium formed with a track and pre-pits, the track having a wobble, the pre-pits being in a predetermined phase relation with the wobble of the track. The apparatus comprises a pickup for reproducing a signal from the recording medium; a limiter for limiting an amplitude of the signal reproduced by the pickup in response to a limiting level, and thereby processing the signal reproduced by the pickup into a limiting-resultant signal; a filter for suppressing components of the limiting-resultant signal generated by the limiter, and thereby processing the limiting-resultant signal into a filtering-resultant signal, the components having specified frequencies and being caused by the pre-pits; a phase adjuster for adjusting a phase of the filtering-resultant signal generated by the filter, and thereby changing the filtering-resultant signal generated by the filter into an adjustment-resultant signal; first means for generating the limiting level for the limiter in response to the adjustment-resultant signal generated by the phase adjuster; and second means for extracting, from the filtering-resultant signal generated by the filter, a signal caused by the wobble of the groove.
A fourth aspect of this invention is based on the third aspect thereof, and provides an apparatus wherein the phase adjuster comprises means for adjusting the phase of the filtering-resultant signal by a variable quantity.
A fifth aspect of this invention provides an apparatus for recording and reproducing information on and from a recording medium formed with a track and pre-pits, the track having a wobble, the pre-pits being in a predetermined phase relation with the wobble of the track. The apparatus comprises a pickup for reproducing a signal from the recording medium; a first amplifier for amplifying the signal reproduced by the pickup into a first amplification-resultant signal at a gain corresponding to a factor of X, where X denotes a predetermined positive number; a limiter for limiting an amplitude of the first amplification-resultant signal generated by the first amplifier in response to a limiting level, and thereby processing the first amplification-resultant signal into a limiting-resultant signal; a low pass filter for suppressing components of the limiting-resultant signal generated by the limiter, and thereby processing the limiting-resultant signal into a first filtering-resultant signal, the components having specified frequencies and being caused by the pre-pits; first means for generating the limiting level for the limiter in response to the first filtering-resultant signal generated by the low pass filter; a high pass filter for processing the first filtering-resultant signal generated by the low pass filter into a second filtering-resultant signal; second means for converting the second filtering-resultant signal generated by the high pass filter into a signal corresponding to the wobble of the groove; a second amplifier for amplifying the first filtering-resultant signal generated by the low pass filter into a second amplification-resultant signal at a gain corresponding to a factor of 1/X; and a comparator for comparing the signal reproduced by the pickup and the second amplification-resultant signal generated by the second amplifier to generate a signal corresponding to the pre-pits.
A sixth aspect of this invention is based on the fifth aspect thereof, and provides an apparatus wherein the limiting level for the limiter is variable.
A seventh aspect of this invention is based on the fifth aspect thereof, and provides an apparatus further comprising third means for controlling the limiting level for the limiter in response to whether the apparatus is operating in a recording mode or a reproducing mode.